Heat exchangers are commonly constructed from stacks or bundles of spaced-apart flat tubes, in which the interiors of the tubes define flow passages for a first fluid and in which spaces between adjacent tubes define flow passages for a second fluid. The flat tubes may comprise pairs of flat plates joined together at their margins.
The ends of the tubes in the stack or bundle are usually retained by a perforated header or tube sheet and the spaces between the plates may be at least partially enclosed by a housing. Examples of exhaust gas heat exchangers of this type are shown in U.S. Pat. No. 6,293,337 (Strahle et al.) and in U.S. Pat. No. 6,269,870 (Banzhaf et al.).
It is also known to construct heat exchangers comprising bundles of spaced-apart flat tubes in which the need for a perforated header is eliminated. An example of a heat exchanger having this type of construction is described in U.S. Pat. No. 6,321,835 (Damsohn et al.). In this patent, the ends of the heat exchanger tubes are expanded in width and height relative to the central portions of the tubes. The tube ends are sealed directly to one another and to the housing, thereby eliminating the need for a perforated header.
There remains a need to provide stacked-tube heat exchangers of simplified, reliable construction and to improve and simplify processes for manufacturing such heat exchangers.